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Wasting-Disease Culprit May Be Tongue

The mystery of how deer and elk spread chronic wasting disease from one animal to another may be solved: their tongues are infectious.

When the animals lick or slobber on each other -- a fairly common occurrence, especially among elk -- the agent that causes the fatal disease may be shed from their tongues via saliva. And when they graze, leaving sloughed-off tongue cells and saliva in grass and soil, the disease could be widely transmitted.

Dr. Richard Bessen, an associate professor of veterinary molecular biology at Montana State University in Bozeman, discovered the infectious agent, called a prion, in deer and elk tongues. Details of disease transmission still need to be worked out, he said, but he believes the prions in saliva are significant in the growing national epidemic of the disease.

Since it was first identified two decades ago in deer in Colorado, chronic wasting disease has spread to a dozen states (including New York) and two Canadian provinces.

Last month officials in West Virginia and Alberta announced their first cases of the malady in wild deer, an indication that the problem is still spreading. And last week the Colorado Department of Wildlife said it had found it in a wild bull moose for the first time.

Deer, elk and moose are all members of the cervid family and share genetic traits. But unlike deer and elk, moose are solitary animals that roam alone or in cow-calf pairs.

Chronic wasting disease belongs to a group of fatal maladies called transmissible spongiform encephalopathies, which include mad cow disease and sheep scrapie.

Infectious prions are also found in sheep tongues, Dr. Bessen said. He presented his findings at the Second International Chronic Wasting Disease Symposium held in Madison, Wis., in July. Results should be published in the next few months.

The findings "are pretty convincing," said Dr. Patrick Bosque, a neurologist and expert on prion diseases at the Denver Health Medical Center, who added, "Up to now, no one has been able to show how the disease spread from deer to deer."

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The United States Department of Agriculture, which provided the tissue samples used by Dr. Bessen, declined to comment until the findings are accepted for publication in a scientific journal.

The details of how prions get into certain animals have been worked out, Dr. Bessen said. When cows, sheep, monkeys or other animals eat feed contaminated with prions, the infectious particles land in their guts. From there they invade lymph tissue and nerves that travel from the gut into the spinal cord and the brain.

But wild deer and elk are not likely to eat contaminated feed. Somehow the disease is spread from animal to animal, via the environment.

The question is how prions move from the brain to peripheral tissues and how are they shed.

"We decided to focus on the tongue," Dr. Bessen said. It is a muscle with extensive nerve connections to the brain and the central nervous system. Some nerves make direct connections with taste cells, which shed into saliva. And a type of tonsil tissue found at the back of the tongue is a potential target for prions.

Experiments clearly show that the tongues of elk and deer contain prions, Dr. Bessen said. Nasal tissue is also infected. Other experiments with hamsters show that prions travel specifically to taste buds on the tongue, raising the possibility that the same happens in deer and elk.

British scientists are also concerned about the tongues of cattle infected with mad cow, Dr. Bessen said. In April, Dr. Gerald Wells of the Veterinary Laboratories Agency in Weybridge, England, reported trace amounts of prions found in palantine tonsil, a type of tissue in the pharynx, near the back of the tongue. Slaughterhouses remove tonsils, he said, but they often allow the root of the tongue, which may also be infected, into the food supply.

So far there is no evidence that people exposed to chronic wasting disease are in danger of contracting it or any related prion disease.

Hunters are advised to take whole deer or elk heads to centrally run state laboratories for prion testing. Otherwise they leave the head and entrails in the wild, where scavengers scatter the remains.